An exceptional-point (EP) enhanced fiber-optic bending sensor is reported. The sensor is implemented based on parity-time (PT)-symmetry using two coupled Fabry-Perot (FP) resonators consisting of three cascaded fiber Bragg gratings (FBGs) inscribed in an erbium-ytterbium co-doped fiber (EYDF). The EP is achieved by controlling the pumping power to manipulate the gain and loss of the gain and loss FP resonators. Once a bending force is applied to the gain FP resonator to make the operation of the system away from its EP, frequency splitting occurs, and the frequency spacing is a nonlinear function of the bending curvature, with an increased slope near the EP. Thus, by measuring the frequency spacing, the bending information is measured with increased sensitivity. To achieve high-speed and high-resolution interrogation, the optical spectral response of the sensor is converted to the microwave domain by implementing a dual-passband microwave-photonic filter (MPF), with the spacing between the two passbands equal to that of the frequency splitting. The proposed sensor is evaluated experimentally. A curvature sensing range from 0.28 to 2.74 m^?1 is achieved with an accuracy of 7.56×10^?4 m^?1 and a sensitivity of 1.32 GHz/m^?1, which is more than 4 times higher than those reported previously.

Parity‐time (PT) symmetry breaking offers mode selection capability for facilitating single‐mode oscillation in the optoelectronic oscillator (OEO) loop. However, most OEO implementations depend on discrete devices, which impedes proliferation due to size, weight, power consumption, and cost. In this work, we propose and experimentally demonstrate an on-chip tunable PT‐symmetric OEO. A tunable microwave photonic filter, a PT‐symmetric mode‐selective architecture, and two photodetectors are integrated on a silicon‐on‐insulator chip. By exploiting an on‐chip Mach–Zehnder interferometer to match the gain and loss of two mutually coupled optoelectronic loops, single‐mode oscillation can be obtained. In the experiment, the oscillation frequency of the on-chip tunable PT‐symmetric OEO can be tuned from 0 to 20 GHz. To emulate the integrated case, the OEO loop length is minimized, and no extra-long fiber is used in the experiment. When the oscillation frequency is 13.67 GHz, the single‐sideband phase noise at 10-kHz offset frequency is -80.96 dBc / Hz and the side mode suppression ratio is 46 dB. The proposed on-chip tunable PT‐symmetric OEO significantly reduces the footprint of the system and enhances mode selection.

In order to realize the ultrastrong absorption of graphene with electrical modulation properties, we designed a composite structure of graphene and parity-time (PT) symmetry photonic crystal, which is achieved by placing the graphene layer on the top layer of the PT symmetry photonic crystal. In this paper, the absorption properties of graphene and the electrical modulating properties of the structure were theoretically analyzed based on the transfer matrix method. The result shows that the proposed structure can achieve the absorption of 31.5 dB for the communication wavelength of 1550 nm; meanwhile, by setting the electric field intensity to ±0.02V/nm, the absorption of graphene can be largely modulated to realize an electrically switchable effect, the modulation depth of graphene absorption can reach nearly 100%, and the operation speed is also close to 8.171 GHz. This investigation provides a novel approach to design graphene-based optoelectronic devices and optical communication devices.